Investigating dense suspensions in yield stress emulsions
Lead Research Organisation:
University of Edinburgh
Department Name: Sch of Physics and Astronomy
Abstract
The rheological properties of high particle volume fraction suspensions have been found to possess interesting properties such as frictional contact based shear thickening. Emulsions are widely used materials which can have different properties based on the volume fraction and packing of the droplets. The interplay between these two systems, where a well defined emulsion acts as a yield stress background for a dense suspension, is not well defined and could lead to interesting properties.
People |
ORCID iD |
| Wilson Poon (Primary Supervisor) | |
| Lewis McHale (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/R511912/1 | 01/10/2017 | 31/12/2022 | |||
| 1942612 | Studentship | EP/R511912/1 | 01/09/2017 | 31/08/2021 | Lewis McHale |
| Description | This work has, and continues to, investigate the presence of yield stresses in dense suspensions. This has included both emulsions as a background and also yield stresses in pure suspensions. We have found that it is difficult to gain both shear thickening and yield stresses in emulsion systems due to the high volume fractions needed for both phases however they can have "Strengthening" effects on each other where history dependence and mixing methods can have large impacts on the rheology and stability. A pure particle suspension has been investigated, this consists of a commercially available industrial particle as the core component of the suspension, this material is interesting as it displays yield stress behaviour where this would not be expected. We have discovered that by introducing a surfactant to this system in is possible to finely tune the suspension between yield stress and shear thickening rheologies with a range of intermediate states, which has not been previously seen. This allows a non-model system which has particles that are not well controlled to be used to investigate multiple rheologies and find the underlying forces in the suspension. We have applied a new model of suspension flow, which has been proposed theoretically for model system by another member of the research group, to these experimental results for the first time and found that all of the flow curves can be well described. Using this model it is possible to identify the type and amount of particle-particle interactions taking place in the system at any given time and applied stress, this allowed us to discover that one type of interaction is heavily dependent on surfactant concentration while the other is relatively independent, this prompted the proposal of a "Patchy particle" theory that suggests the surface forces of the particle may not be uniform and so would explain these unexpected findings. Using electron microscopy and Energy Dispersive X-Ray Spectroscopy on these suspensions we are able to probe the surface topography and elemental composition of these particles and discovered that there are variations in the elemental composition of the particle surface which would lead to areas that are adhesive and repulsive which supports the proposed "patchy particle" theory. This is a novel technique in this field as it is not common practice to pair rheology to surface science techniques, what this approach has allowed us to do is to gain an understanding of what was a non-model suspension from the elemental composition which sets the particle interactions and so produces the macroscopic flow. |
| Exploitation Route | Combining emulsions with particles is a model system for drilling fluids and so probing the limits of how far you can push the volume fractions of these systems before they become unstable is useful for the industry as these multi-phase systems are widespread and require high fractions of multiple componants. The use of the "constraints" model for real systems has not been used before and so by showing it can work well for a non-model industrial system allows this model to be expanded to other real suspensions, in this work i have also identified and presented the key factors that this model would give you such as "Critical Stresses" this could be used in research to identify the stresses that interactions are happening at and so the microscale particle interactions present at any point in a suspension under stress. For industrial use this proves that this model can be applied to industrial systems to help them identify the optimal stresses and help them target the key factor to tune in formulation . The use of surface science techniques in conjunction with rheological experiments and modelling is a novel approach and use of methods and could be taken forward my many researchers to understand their systems and identify the fundamental interactions that happen on the smallest scales that control the macroscopic properties of a suspension. Many industries use suspensions from drilling fluids in the oil industry, cement, food and to paint just to name a few and so understanding and controlling these suspensions is of critical importance for efficiency, preventing failures such as blockage during flow and reducing the environmental impact of these industries by better formulating these systems. The particular industrial material investigated is commonly used as a filler in many industries such as a component in some model cements. |
| Sectors | Agriculture, Food and Drink,Construction,Environment,Manufacturing, including Industrial Biotechology |